Uniform suspensions of single cells enriched in a single type are conventionally prepared by centrifugation, by preferential attachment to specially treated surfaces, or by differential resistance to a cytotoxic agent. These methods are not generally applicable to all cell separations, nor are they feasible when the desired type of cell is a small minority in the mixture. A new bulk method involving magnetic affinity heads which attach to cells and remove them from the suspension in an external magnetic field has been shown to yield populations 99% homogeneous with respect to their cell-surface marker. Further research on this method is proposed to determine how the new separations relate to those performed by fluorescence-activated cell sorting, which is slower and often prohibitively expensive. The parameters of the method of preparing the magnetic microspheres of the apparatus used in the separation and of model cell populations separated on the basis of various membrane markers which bind to ligands with different affinities will be investigated. The microspheres will be encapsulated in hydrogels by polymerization of hydrophilic monomers. IgG and lectins will be covanently attached as ligands. A disulfide bond will be introduced to provide a reversible ligand.